For consistency, and because clang-tidy can't figure out if a define is an
include guard unless it ends the file.

Not all of these actually show up in the output, but it's unnecessary to use
these in Markdown anyway.

This was a mistake, and it's arguable which URI was correct before.  It was
supposed to be "StateChanged" since the name of URIs should stand
alone (ignoring the conventional prefix, even though this has been screwed up
in several places in the past).  Normally, the specification in Turtle is
considered canonical for URIs, but in this case, the URI defined in the
corresponding header used "StateChanged" (both in name and value), as did all
the news.  Really everything except the subject in the metadata.

So, consider this a documentation bug, and fix the URI in the
spec/documentation to match the implemented one.